1. Field of Invention
The present invention relates to a driving method and a drive circuit for an electrooptic device in which a gradational display control is performed by a subfield drive scheme, as well as to an electrooptic device, and electronic equipment.
2. Description of Related Art
Currently, electrooptic devices, such as, liquid-crystal display devices each employing a liquid crystal as an electrooptic material, are extensively used in the display portions of various information processing equipment, liquid-crystal television sets, etc. as display devices which replace cathode ray tubes (CRTs). Such electrooptic devices can be constructed of an element substrate which is provided with pixel electrodes arrayed in the shape of a matrix, switching elements, such as TFTs (Thin Film Transistors), connected to the pixel electrodes, etc., an opposing substrate which is formed with a counter electrode opposing to the pixel electrodes, and a liquid crystal being an electrooptic material which is packed between both the substrates. A display mode of the electrooptic device in such a construction includes “normally white” being a mode which presents a white display in a state where a voltage is not applied (OFF state), and “normally black” being a mode which presents a black display in the state. Now, the operation of presenting a gradational display in the case where the display mode of the electrooptic device is the normally-black mode will be explained.
In the above construction, when a scanning signal is applied to each switching element through a scanning line, the pertinent switching element falls into a conductive state. When, under the conductive state, a picture signal of a voltage corresponding to a gradation is applied to each pixel electrode through a data line, charges corresponding to the voltage of the picture signal are stored in the pertinent pixel electrode and counter electrode. Even when the pertinent switching element is brought into an OFF state after the storage of the charges, the charges in the pertinent electrodes are kept stored by the capacitativeness of the liquid crystal layer itself, a storage capacitance, etc. When, in this manner, each switching element is driven, and the quantity of charges to be stored is controlled in correspondence with the gradation, the oriented state of the liquid crystal varies with every pixel, and hence, the density varies with every pixel. It is therefore possible to present the gradational display.
Additionally, in a case where the display mode of the electrooptic device is the normally-white mode, a similar effect is obtained in such a way that the state of the voltage is changed from the OFF state into an ON state in the above operation.
In the above operation, it may be in a partial period of time that the charges are stored in the liquid crystal layer of each pixel, so the following controls are possible:
(1) Sequentially selecting the individual scanning lines by a scanning line drive circuit
(2) Supplying picture signals to the data lines by a data line drive circuit in the period of the selection of the scanning line; and
(3) Sampling picture signals from the data lines.
Owing to the controls (1), (2) and (3), time-division multiplexing drive is realized in which the scanning line and the data line are respectively made common to pluralities of pixels.
However, the picture signals which are applied to the data lines are voltages corresponding to gradations, namely, analog signals. Therefore, D/A conversion circuits, operational amplifiers etc. are required as the peripheral circuits of the electrooptic device, thus incurring a high cost for the whole device. In addition, nonuniformity in display appears due to discrepancies in the characteristics of the D/A conversion circuits, the operational amplifiers etc. and in various wiring resistances etc., resulting in the problem that a display of high quality is very difficult to obtain. This problem becomes more apparent in the case of presenting a display of high definition.